diff --git a/test/conf/cassandra-converters-special-cases-old-names.yaml b/test/conf/cassandra-converters-special-cases-old-names.yaml
index 821429a209..b3e26d8a40 100644
--- a/test/conf/cassandra-converters-special-cases-old-names.yaml
+++ b/test/conf/cassandra-converters-special-cases-old-names.yaml
@@ -5,4 +5,6 @@
 sstable_preemptive_open_interval_in_mb: -1
 index_summary_resize_interval_in_minutes: -1
 cache_load_timeout_seconds: -1
+commitlog_sync_group_window_in_ms: NaN
+credentials_update_interval_in_ms: -1
 
diff --git a/test/conf/cassandra-converters-special-cases.yaml b/test/conf/cassandra-converters-special-cases.yaml
index 96bba0ef73..f3f896ac23 100644
--- a/test/conf/cassandra-converters-special-cases.yaml
+++ b/test/conf/cassandra-converters-special-cases.yaml
@@ -5,4 +5,6 @@
 sstable_preemptive_open_interval:
 index_summary_resize_interval:
 cache_load_timeout: 0s
+commitlog_sync_group_window: 0ms
+credentials_update_interval:
 
diff --git a/test/unit/org/apache/cassandra/config/YamlConfigurationLoaderTest.java b/test/unit/org/apache/cassandra/config/YamlConfigurationLoaderTest.java
index 350a84c1ff..06be1dc209 100644
--- a/test/unit/org/apache/cassandra/config/YamlConfigurationLoaderTest.java
+++ b/test/unit/org/apache/cassandra/config/YamlConfigurationLoaderTest.java
@@ -131,21 +131,25 @@ public class YamlConfigurationLoaderTest
         Map<String, Object> map = new HashMap<>();
         map.put("sstable_preemptive_open_interval", null);
         map.put("index_summary_resize_interval", null);
+        map.put("credentials_update_interval", null);
 
         Config c = YamlConfigurationLoader.fromMap(map, true, Config.class);
         assertThat(c.sstable_preemptive_open_interval).isNull();
         assertThat(c.index_summary_resize_interval).isNull();
+        assertThat(c.credentials_update_interval).isNull();
 
         map = ImmutableMap.of(
         "sstable_preemptive_open_interval_in_mb", "-1",
         "index_summary_resize_interval_in_minutes", "-1",
-        "cache_load_timeout_seconds", "-1"
+        "cache_load_timeout_seconds", "-1",
+        "credentials_update_interval_in_ms", "-1"
         );
         c = YamlConfigurationLoader.fromMap(map, Config.class);
 
         assertThat(c.sstable_preemptive_open_interval).isNull();
         assertThat(c.index_summary_resize_interval).isNull();
         assertThat(c.cache_load_timeout).isEqualTo(new DurationSpec.IntSecondsBound("0s"));
+        assertThat(c.credentials_update_interval).isNull();
     }
 
     @Test
diff --git a/test/unit/org/apache/cassandra/db/virtual/SettingsTableTest.java b/test/unit/org/apache/cassandra/db/virtual/SettingsTableTest.java
index aba2a1d61a..a5c69cd240 100644
--- a/test/unit/org/apache/cassandra/db/virtual/SettingsTableTest.java
+++ b/test/unit/org/apache/cassandra/db/virtual/SettingsTableTest.java
@@ -60,6 +60,8 @@ public class SettingsTableTest extends CQLTester
         config.sstable_preemptive_open_interval = null;
         config.index_summary_resize_interval = null;
         config.cache_load_timeout = new DurationSpec.IntSecondsBound(0);
+        config.commitlog_sync_group_window = new DurationSpec.IntMillisecondsBound(0);
+        config.credentials_update_interval = null;
         table = new SettingsTable(KS_NAME, config);
         VirtualKeyspaceRegistry.instance.register(new VirtualKeyspace(KS_NAME, ImmutableList.of(table)));
         disablePreparedReuseForTest();
@@ -130,6 +132,18 @@ public class SettingsTableTest extends CQLTester
         assertRowsNet(executeNet(q), new Object[] {"cache_load_timeout", "0s"});
         q = "SELECT * FROM vts.settings WHERE name = 'cache_load_timeout_seconds';";
         assertRowsNet(executeNet(q), new Object[] {"cache_load_timeout_seconds", "0"});
+
+        // test MILLIS_DURATION_DOUBLE converter
+        q = "SELECT * FROM vts.settings WHERE name = 'commitlog_sync_group_window';";
+        assertRowsNet(executeNet(q), new Object[] {"commitlog_sync_group_window", "0ms"});
+        q = "SELECT * FROM vts.settings WHERE name = 'commitlog_sync_group_window_in_ms';";
+        assertRowsNet(executeNet(q), new Object[] {"commitlog_sync_group_window_in_ms", "0.0"});
+
+        //test MILLIS_CUSTOM_DURATION converter
+        q = "SELECT * FROM vts.settings WHERE name = 'credentials_update_interval';";
+        assertRowsNet(executeNet(q), new Object[] {"credentials_update_interval", null});
+        q = "SELECT * FROM vts.settings WHERE name = 'credentials_update_interval_in_ms';";
+        assertRowsNet(executeNet(q), new Object[] {"credentials_update_interval_in_ms", "-1"});
     }
 
     private String getValue(Property prop)